ECM Power Supply, Checking

ECM Power Supply, Checking

Special tools, testers and auxiliary items required

• (VAG1526A)

• (VAG1594A)

• (VAG1598/31)

Test requirements

• Fuses for engine electronics OK

• Battery voltage at least 12.7 V

• Alternator OK

Test sequence

- Connect test box (VAG1598/31) to wiring harness for engine control module; do not connect engine control module. Refer to => [ Wiring and Component Check with Test Box VAG 1598/31 ] Wiring and Component Check With Test Box VAG 1598/31.

- Switch ignition on.

• The positive voltage supply to the engine control module is provided via terminal 3 (terminal 15) and terminal 62 (terminal 30).

• The ground connection to the engine control module is provided via terminal 1 and terminal 2.

- Connect multimeter as follows to measure voltage:





• Specified value: approx. battery voltage

- Connect multimeter as follows to measure voltage:





- Switch ignition on.

• Specified value: approx. battery voltage

If the specified values are not obtained:

- Check wiring connections.

- Connect multimeter as follows to measure voltage:





* The Motronic Engine Control Module (ECM) power supply relay (J271) carries voltage on terminal 121 of engine control modules after switching off the ignition for up to 15 minutes.

- Switch ignition on.

• Specified value: approx. battery voltage

If specified value is not attained:

- Check wiring connections.

- Check Motronic Engine Control Module (ECM) power supply relay (J271). Refer to => [ ECM Power Supply Relay, Checking ] ECM Power Supply Relay, Checking.